1. Field of the Invention
The present invention relates to a control device of an automatic transmission for vehicles.
2. Description of the Prior Art
A conventional control device of an automatic transmission for vehicles is disclosed, for example, in Japanese Patent Application Laid-open Publication No. 4-351356. This automatic transmission comprises a main transmission mechanism arranged coaxially with a torque converter and a sub transmission mechanism arranged in parallel with the main transmission mechanism. In this automatic transmission, the control device achieves a plurality of gear positions by engaging and disengaging friction elements such as planetary gear mechanisms, clutches, brakes and one-way clutches.
In the control device of the automatic transmission mechanism, an automatic transmission control unit (hereinafter referred to as an ATCU) determines a gear position suitable for driving conditions, on-off controls solenoid valves in the control device, switches shift valves by an oil pressure supplied through the solenoid valves, and changes the gear positions by supplying and releasing oil pressure to and from the friction elements by the shift valves.
An ordinary control device has a parking range, a rear driving range (hereinafter referred to as a R range), a neutral range, an automatic shift driving range (hereinafter referred to as a D range), a 3 range in which a vehicle is driven forward at a first, second or third speed gear position, a 2 range in which a vehicle is driven forward at the first or second speed gear position, a 1 range in which the vehicle is driven forward only at the first speed gear position.
The conventional control device of the automatic transmission cuts a reverse driving force from wheels and does not operate an engine brake at a slow speed gear positions in the D range in order to prevent a shock resulting from an automatic shift from a high speed gear position to a low speed gear position.
If the ATCU malfunctions, however, it becomes impossible to control the solenoid valves for setting a gear position and this fixes the state of the shift valves for use in changing the gear positions.
If the ATCU malfunctions to fix the gear position at a high speed gear position or the like, it is possible to continue driving the vehicle that is still running. Once the vehicle stops running, however, it is difficult to start the vehicle again.
It is therefore an object of the present invention to provide an improved control device of an automatic transmission, which prevents the shock resulting from the shift even if there is a malfunction during the driving and which easily starts the vehicle after it stops.
The above object can be accomplished by providing a control device of an automatic transmission, which has an automatic shift range for automatically selecting a gear position according to driving conditions of a vehicle, and a manual setting range for manually changing gear positions and having at least a low speed engine brake range in which the vehicle is driven at a lowest speed gear position with an engine brake being operable, the control device of the automatic transmission comprising: an operating pressure control circuit for controlling an operating pressure supplied to and released from friction elements for selectively changing power transmission routes of a transmission mechanism; wherein the operating pressure control circuit comprises: a plurality of shift valves for changing supply and release channels for supplying and releasing the operating pressure to and from the friction elements according to the selected gear position; first signal pressure generating means for supplying and releasing a signal pressure for controlling shift positions of the shift valves; shift control means for controlling the first signal pressure generating means according to the selected gear position; second signal pressure generating means for supplying a low speed range signal pressure if a low speed engine brake range is manually designated; first fail range achieving means for achieving a lowest speed gear position at which the vehicle is driven with the engine brake being operable if the shift control means fails and if the second signal pressure generating means supplies a low speed range signal pressure; and second fail range achieving means for achieving a predetermined gear position other than low speed gear positions if the shift control means fails and if the second signal pressure generating means does not supply low speed range signal pressure.
Accordingly, even if the control unit as the shift control means, or the like, malfunctions while the vehicle is running in a range other than the low speed engine brake range, the second fail range achieving means achieves a predetermined gear position other than low speed gear positions since there is no supply of low speed range signal pressure from the second signal pressure generating means. Therefore, the gear position never shifts to the lowest speed gear position at which the vehicle is driven with the engine brake being operable. This prevents the shock due to the shift.
If the control unit as the shift control means, or the like, malfunctions while the vehicle is driven in the low speed engine brake range, there is the supply of the low speed range signal pressure from the second signal pressure generating means. Therefore, the first fail range achieving means achieves the lowest speed gear position at which the engine brake is operable.
Moreover, even if the control unit or the like malfunctions to thereby stop the vehicle, the low speed engine brake range is selected so as to shift the gear position to the lowest speed gear position at which the vehicle is driven with the engine brake being operable. Thus, the vehicle can easily be started.
Thus, if the control unit or the like malfunctions, the low speed engine brake range is selected to start the vehicle at the lowest speed gear position with the engine brake being operable. When a vehicle speed is increased, the range is switched to another range to cause the vehicle to run by itself at a predetermined gear position other than the low speed gear positions.
The above object can also be accomplished by providing a control device of an automatic transmission, which has automatic shift ranges for automatically selecting a gear position according to driving conditions of a vehicle, and manual setting range for manually changing gear positions and having at least a low speed engine brake range in which the vehicle is driven at a lowest speed gear position with an engine brake being operable, the control device of the automatic transmission comprising: a first shift valve, a second shift valve and a third shift valve for changing the connecting state of oil channels supplying an oil pressure to friction elements for setting the gear position; a first switching oil channel for supplying an oil pressure for changing the connecting state of the first shift valve; a first solenoid valve that is on-off controlled in such a manner as to supply an oil pressure to the first switching oil channel in a state of being on; a second switching oil channel for supplying an oil pressure for changing the connecting state of the second shift valve; a second solenoid valve that is on-off controlled in such a manner as to supply an oil pressure to the second switching oil channel in a state of being on in normal operation; a third switching oil channel for supplying an oil pressure for changing the connecting state of the third shift valve, and a third solenoid valve (SC) that is on-off controlled in such a manner as to supply an oil pressure to the third switching oil channel in a state of being on in normal operation; a shift control part for controlling the ON/OFF state of the first, second and third solenoid valves according to a designated range in such a manner as to turn on the first, second and third solenoid valves if the lowest speed gear position is selected in the automatic shift dive range, and turn off the first solenoid valve and turn on the second and third solenoid valves if the lowest speed gear position at which the vehicle is driven with the engine brake being operable is selected; the shift control part turning on at least one of the first, second and third solenoid valves in normal operation; a manual valve for selectively connecting oil pressure sources to oil channels by manual operation; a low speed gear position selecting channels which is supplied with an oil pressure from the manual valve when the low speed engine brake range is selected; a failsafe valve for connecting low speed gear position selecting channels with the second and third switching oil channels if the first, second and third solenoid valves are turned off; and wherein the first, second and third shift valves connect to the friction elements in such a manner as to set a predetermined gear position other than the low speed gear positions if the oil pressure is not supplied to the first, second and third switching oil channels.
Accordingly, no oil pressure is supplied to the first, second and third switching oil channels when the first, second and third solenoid valves are turned off while the vehicle is driven in the automatic shift driving range or the manual setting range other than the low speed engine brake range. Thus, the gear position other than the low speed gear positions is set. Therefore, even if the control unit or the like malfunctions while the vehicle is driven in the automatic shift driving range or the manual setting range other than the low speed engine brake range, the gear position never shifts to the lowest speed gear position at which the vehicle is driven with the engine brake being operable. This prevents the shock due to the shift.
If all the solenoid valves for changing the gear positions are turned off while the vehicle is driven in the low speed engine brake range, the oil pressure is supplied from the manual valve to the second and third switching oil channels through the first oil channel, the failsafe valve and the second oil channel. This shifts the gear position to the lowest speed gear position at which the vehicle is driven with the engine brake being operable.
If the vehicle stops running due to the malfunction of the control unit or the like, the gear position can be shifted to the lowest speed gear position by designating the low speed engine brake range.
If the control device or the like malfunctions, the vehicle is started in the low speed engine brake range, which is then switched to another range when the vehicle speed is increased. Therefore, the vehicle can run by itself at a gear position other than the low speed gear positions.
In the normal operation, the first, second and third solenoid valves are turned off when the first speed gear position in the automatic shift driving range, i.e., the lowest speed gear position at which the engine brake is not operable is selected.
While a gear position other than the lowest speed gear position is selected, at least one solenoid valve is off. Thus, at least two solenoid valves are turned off when one of the solenoid valves that should be normally on is turned off due to the breaking of wire.
Accordingly, even if one of the solenoid valves that should be normally on is turned off the gear position does not shift to the lowest speed gear position at which the engine brake is operable, and shock resulting from the shift is prevented.
Particularly in the case where the automatic shift driving range has the first speed gear position as the lowest speed gear position through the fifth speed gear position as the highest speed gear position, the gear position can be switched to the fourth speed gear position if no oil pressure is supplied to the first, second and third switching oil channels. By this feature, the shock resulting from the shift is surely prevented, since the gear position shifts to a higher speed gear position when the control unit or the like malfunctions while the vehicle is running in a low speed range other than the low speed engine brake range or in the automatic shift driving range.